Assembly for sealing a sliding interface

ABSTRACT

An assembly is disclosed for sealing the sliding interface between two objects capable of sliding or moving with respect to one another, but where the sliding interface must provide a substantial seal against pressure loss therethrough, such as where an assembly seals the sliding interface between a piston and a cylinder or between a rod and a bushing. Although some features of this invention would be beneficial in applications using a liquid lubricant, the invention is particularly beneficial in applications not using a liquid lubricant, where the materials of the piston, cylinder, and sealing system are chosen additionally for their ability to provide self-lubrication as they slide over each other, while providing low friction and a low wear rate during sliding.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. provisional patent applicationSer. No. 61/444,653, filed on Feb. 18, 2011, which is herebyincorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of sealing of slidinginterfaces. More particularly, the present invention relates to thefield of sealing of sliding interfaces, such as that existing between acylinder and a piston reciprocating therein, or between a bushing and arod reciprocating within an aperture through the bushing, where adifference in pressure exists between or across opposed faces orsurfaces of the moving member.

2. Background of the Art

Sliding seal interfaces are used to enable the transfer of energy, suchas from combustion or from temperature or pressure changes of a gas orfluid in an enclosed volume, by enabling a member such as a piston tomove relative to a cylinder, and thus expand or contract the volumeenclosed by the cylinder and piston surfaces in response to suchcombustion or pressure or temperature changes, and thereby enable theenergy, evidenced for example by an increase in fluid pressure in avolume bounded by a piston and a cylinder, to be reduced in that volumeby increasing the volume within which the fluid is present, resulting inuseful movement of the piston to transfer energy to a useful output,such as a shaft used to drive an electrical generator, a wheel, or othermechanical or electromechanical device.

There exist several fundamental issues with the recovery of energy froma reciprocating piston driven by pressure-volume energy changes in acylinder. To maximize the energy recovered by a change in pressurewithin the volume bounded by the cylinder and piston surfaces, leakageof the fluid under pressure past the interface between the piston outersurface and the adjacent cylinder inner surface must be minimized, whichdictates a tight seal, yet friction (and wear) caused by physicalcontact of the piston with the cylinder must also be minimized, whichdictates little or no contact between moving parts. The same paradigm ispresent where the converse situation is present, where energy is beingtransferred from a mechanical apparatus into a fluid, such as where afluid is being compressed by reducing its volume within apiston-cylinder system. In either situation, loss of fluid underpressure through the interface, as well as friction at the interface,reduces the energy recovered from or put into the fluid, and hence theefficiency of the device.

One known mechanism for sealing a piston-cylinder interface is to employa split ring, also known as a Ramsbottom seal, in a groove in the pistonwall such that the seal moves with the piston and seals across thepiston-cylinder interface. The seal is commonly, for example, a squarecut split metal ring, which is received within a mating square cutgroove in the outer cylindrical surface of the piston, and the freediameter of the ring or seal is larger than the inner diameter of thecylinder, which ensures expansion or bias of the outer surface of thering toward the inner circumferential wall of the cylinder. Oil or otherlubricant is commonly, but not always, used to lubricate the contactarea between the seal and the inner wall of the cylinder, which providesa mechanism to remove heat from the sliding interface and reducefriction where the outer face of the ring rides on a thin film of oiland not directly in contact with the cylinder wall. However, inapplications where lubricants cannot or should not be used, for example,where a seal must be maintained across alternating low pressure and highpressure sides of a piston located in a cylinder used in a Stirlingengine, the lack of lubrication contraindicates the use of a Ramsbottomor other contact-type seal, because of the high contact friction betweenthe seal and cylinder wall, which leads to energy losses, and the highwear of the ring and/or the cylinder wall, which will require frequentreplacement of one or both. These issues have limited the application ofa simple Ramsbottom seal arrangement in such no- or low-lubricantapplications.

One mechanism which has been used to provide a non-lubricated slidingseal is a clearance seal between the outer circumferential surface ofthe piston and inner circumferential surface of the cylinder withinwhich the piston reciprocates. A clearance seal is formed by anintended, minute radial gap between the outer circumferential wall ofthe piston and adjacent interior cylinder wall surfaces. In theory, thepiston may reciprocate in the cylinder on a hydrodynamic gas bearingformed by the very thin cushion of a gas or fluid which may be createdbetween the outer circumferential wall of the piston and the innercircumferential wall of the cylinder by their relative motion. Inpractice, however, such a bearing is formed by supplying the gap withpressurized gas, making the bearing a hydrostatic bearing, requiring asupply of this pressurized gas. If it is desired that the piston notcontact the cylinder, but not incur the expense of the hydrostatic gasbearing and associated components to provide pressurization, exactingalignment of the piston with respect to the cylinder is required of themechanism that provides or receives mechanical energy to or from thepiston respectively, to cantilever the piston off of this mechanism intothe cylinder so that the piston moves within the cylinder withouttouching the cylinder wall. Because the clearance seal provides aleakage path between a high and low pressure side of the piston, aninherent energy and efficiency loss is present, exacerbated by theenergy consumed to pressurize a hydrostatic gas bearing if used, but istolerated as an acceptable trade off to enable non-lubricated sealing ofthe piston-cylinder interface.

SUMMARY OF THE INVENTION

The present invention provides a non-lubricated sliding seal wherein aseal member is received within a seal groove in one of a first or asecond member, and the first member moves with respect to the secondmember. The seal ring has a height, a free outer diameter and a freeinner diameter, and is received within a seal groove extending inwardlyof a surface of said first or second member, and faces a surface of theother of said first and second members. The first and second membersabut each other for sliding motion relative to one another, wherein adifference in pressure of a fluid spans the interface therebetween, aclearance gap exists between the first and second members, and fluid atthe higher pressure may enter the clearance gap therebetween. The sealgroove has a height larger than that of the seal ring, and acircumference such that, during relative sliding movement of the firstand second members, the seal ring may move in either direction in whichthe relative sliding motion occurs, but usually opposed to the directionfrom which the higher pressure is present. The circumferential base ofthe seal groove is sized to ensure a gap between the seal ring and thecircumferential base of the seal groove, such that the higher pressuremay communicate through the clearance therebetween and into the sealgroove, and thereby be maintained between the seal ring and the base ofthe seal groove, to bias the face of the seal ring opposite to the baseof the seal groove into sealing engagement with the adjacent facingsurface of the other of the first and second members. Thus, the slidingseal interface provided provides a substantial seal across the first andsecond members from the high to the low pressure sides thereof withoutthe requirement of a lubricant, and without the limitations of aclearance seal. Additionally, the seal lands which form the opposedsides of the seal groove may be a material different from that of theseal ring. Likewise, the seal ring and the member within which the sealgroove is located may comprise a first material, and the member withinor over which the first member moves and the seal lands may comprise asecond material.

In one aspect, the first member is a piston and the second member is acylinder, within which the piston slidingly moves and may reciprocatetherein as pressure is alternatively increased on either side thereof,and the seal groove extends into the outer wall of the piston. Thegroove has opposed lands spaced a height or gap therebetween, and a basehaving a first diameter. The seal ring has a height smaller than theheight or gap of the seal groove, and, in a free state, i.e., where thering is not acted upon by any forces, the seal ring has an outerdiameter greater than the inner diameter of the cylinder and an innerdiameter greater than the diameter of the base of the seal groove.

In an additional aspect, the second member is received within the firstmember, the first member includes an aperture therein though which thesecond member may slidingly move and reciprocate, and the seal groove isreceived within the aperture in the first member and extends into thecircumferential wall of the aperture. The seal groove again has a heightwhich is greater than that of the seal ring, but the inner diameter ofthe seal ring in its free state is less than the outer diameter of thesecond member, and the outer diameter of the seal ring in its free stateis less than the diameter of the base of the seal groove, to ensure thatthe higher pressure, which alternates between the opposed sides of thesecond member, may be present in the space between the base of the sealgroove and the outer diameter of the seal ring.

In a method of sealing a sliding interface, a seal groove is provided ina wall of a first member, which wall is located adjacent to, and moveswith respect to, the wall of a second member, in the presence of apressure difference between opposed sides of one of said first andsecond members, and the seal groove has a height greater than that of aseal ring received therein, and the higher pressure fluid causes theseal ring received in the seal groove to move from the high pressureside of the seal groove to the low pressure side of the seal grooveunder the influence of the alternating pressure. Additionally, themethod may include sizing the seal ring to ensure there is a gap betweenthe seal ring and the base of the seal groove, and influencing the sealring, under the influence of the alternating pressure, to move in adirection opposed to the base of the seal groove toward the secondmember and make contact with it.

In additional aspects, the seal ring, and the first or second memberwithin which the seal groove extends, may be made from a first material,and the opposed faces or lands of the seal groove, and the member (firstor second) which does not include the seal groove therein, may be madeof a second material. Additionally the seal ring groove may be providedin an assembly locatable over, and removable from, an end of one of thefirst or second members, to ease the assembly and replacement thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1 shows a sealed sliding assembly of the present inventioncomprising an assembly for sealing the sliding interface between apiston and a cylinder;

FIG. 1A is a schematic plan view, partially in cutaway, of a pistonhaving the sliding seal assembly of FIG. 1 received in a cylinder.

FIG. 2 shows an alternate embodiment of the present invention comprisingan assembly for sealing the sliding interface between a rod and abushing;

FIG. 3 shows another embodiment of the present invention comprising oneor more springs used in place of the compliant element of FIGS. 1 and 2;and

FIG. 4 shows another embodiment of the present invention, wherein theindividual sealing assembly of FIGS. 1 and 2 is replaced with a ringpack.

DESCRIPTION OF THE EMBODIMENTS

The present invention is an assembly for sealing the sliding interfacebetween two members, for example, between a piston and a cylinder, inwhich the piston must bear a difference in pressure of a fluid acrossits faces and at the same time move by sliding relative to and generallyparallel to and along the axis of the cylinder. It is understood thatthe present invention may likewise be used where the assembly seals thesliding interface between a rod and a bushing, wherein the rod moves bysliding relative to and along the axis of the bushing, or otherapplications where a sliding sealing interface is employed and wherein adegree of pressure isolation across the interface need be maintained.Although some features of this invention would be beneficial inapplications using a liquid lubricant, the invention is particularlybeneficial in applications not using a liquid lubricant. The materialsof the piston, cylinder, and sealing system must therefore be chosenadditionally for their ability to provide self-lubrication as they slidepast or over each other, but which materials may have the limitationthat, to provide low friction and a low wear rate, those materialssliding past or over each other be different from each other. Suchapplications include oil-less gas compressors, gas expanders, andlow-temperature Stirling cycle engines and heat pumps, where featuressuch as low temperature, cleanliness, inert fluid environment, and lackof combustion byproducts favorably promote low friction and a low wearrate of such self-lubricating materials.

FIGS. 1 and 1A show a preferred embodiment of a sealed sliding assembly100 of the present invention useful for sealing a sliding interface 101,wherein a sliding interface 101 between a piston 102 (shown partially,in cutaway in FIG. 1 and fully in plan view of the piston and cutawayview of the cylinder in FIG. 1A) exists between a piston 102 whichreciprocates in a cylinder 104 and provides a seal between opposed upperand lower sides 106, 108 of the piston 102. (In FIG. 1A a skirt assemblyis also shown) A sealing sliding assembly 100 is shown integrallyassembled into a piston 102, which, in this embodiment, reciprocateswithin a cylinder 104. The piston 102 and cylinder 104 are, as shown inFIG. 1A, configured to enable reciprocal motion of the piston 102 withinthe cylinder 104, to thereby impart motion to a connecting rod 107 wherea difference in pressure is maintained on opposed sides of the piston102, or to enable movement of the piston 102 within the cylinder 104 inresponse to motion imparted to the piston 102 by the connecting rod 107.

Piston 102 includes, at least at one end 108 thereof, the connecting rod107, which may be pivotably attached at one end thereof to a boss 109generally centered at one end or face 108 of the piston 102, and atanother end thereof, to a driven component (not shown), such as acrankshaft, camshaft, or other arrangement. The connecting rod 107 mayalso be rigidly attached at one end thereof to the piston 102, likewisegenerally centered at one end or face 108 of the piston 102, and at theother end thereof, to a crosshead (not shown), which is furtherconnected by another connecting rod to a driven component, such as acrankshaft, camshaft, or other arrangement. The sealed sliding assembly100 is, in this embodiment, removably attached adjacent the other faceor end 106 of piston 102, such that the sliding seal assembly 100 may bereadily removed and replaced if servicing or replacement thereof isneeded without removal of the piston 102 from the cylinder.

Referring again to FIG. 1, sliding sealing assembly 100 generallyincludes a seal groove assembly 110, consisting of a clamp ring 164,lands 134 and 136, shim 140, sealing ring 170, and spacer 138, which isremovably attached to end 106 of piston 102 at the perimeter thereof,for ease of replacement if needed. The sliding seal assembly 100 isshown in partial cutaway, revealing the internal structure thereof.Sliding seal assembly 100 generally includes the seal groove assembly110, which is positioned into a circumferential notch 112 extendinginwardly of the end 106 of piston 102 about the outer circumference 114thereof, which assembly is held in place within the notch 112 by a capassembly 116.

Cap assembly 116 includes a cap 118, which may be configured as acircular or annular plate shaped member, having an outer circumference120 which is smaller than the outer circumference 114 of the piston 102,yet is positioned to overhang notch 112. Cap 118 is maintained on theend 106 of piston 102 by a plurality (only one shown) of fasteners 122,in the case of FIG. 1, a plurality of threaded bolts 124 received withinthreaded bores 126 extending inwardly of end 106 of piston 102. Cap 118includes an overhanging portion, 128, into which extends acircumferential positioning groove 130 facing the end 106 of piston 102.A compliant element 132, such as an o-ring, is received and retainedwithin groove 130 and contacts seal groove assembly 110 to retain it inposition on piston 102 within notch 112. Cap 118 is configured, sizedand positioned, with respect to end 106 of piston 102 and notch 112 toprevent release of the seal groove assembly 110 from piston 102. Itshould be understood that although cap 118 is shown in FIG. 1 asincluding only one fastener 122 therewith, FIGS. 1A, 2 and 4 show theapparatus in partial cutaway, and the piston 102 and cap 118 extend assymmetrical cylindrical members, with the cap 118 affixed to the piston102 by a plurality of evenly spaced fasteners 122, typically four ormore fasteners evenly spaced about a bolt circle.

Referring still to FIG. 1, seal groove assembly 110 includes a pair ofopposed first and second lands 134, 136, which are spaced from oneanother by a spacer 138 and a shim 140. Each of the lands has a radialexpanse, as measured from an inner 142 to an outer 144 face thereof,which is slightly less than the depth 146 of the notch 112 in piston102. The diameter prescribing the inner faces 142 of each of the lands134, 136, is sized to be slightly larger than the outer diameter of thenotch 112 within the piston 102, such that the lands 134, 136, may beplaced over the piston 102 end 106 and into notch 112 withoutinterference therewith. Spacer 138 and shim 140, in the embodimentshown, each have an inner diameter approximately equal to that of lands134, 136, but a shorter expanse in the radial direction, such that theouter face 150 of spacer 138 and the outer face 152 of shim 140 form thebase 154 of a seal ring groove 156, and in combination with the facingsurfaces of the lands 134, 136, define the generally rectangular sealring groove.

To maintain the seal groove assembly 110 in position within notch 112, aclamp ring 164 is positioned within the notch 112 and extendssubstantially from first land 134 to the end 106 of piston 102, wherethe complaint element 132 bears against the clamp ring 164 to bias theclamp ring 164 in the direction of the ledge 166 forming a base of thenotch 112, such that the spacer 138 and shim 140 are pressed togetherbetween lands 134, 136, as shown in FIG. 1. The elasticity of thecompliant element 132 maintains the clamp ring 164 in a biased stateagainst the upper land 134 during thermal cycling of the piston 102, tomaintain the integrity of the seal ring groove 156. The force need notbe any greater than that necessary to prevent the parts of the assemblyforming the seal ring groove 156 from separating from one another whenthe fluid pressure is maximally greater on the face 108 of the piston102 opposite the cap 118, or when the force necessary to accelerate themass of the clamped components in the downward direction of the drawingis approaching or at maximum. If the temperature of the fluid, which itis assumed the components will substantially attain during use, iswithin a range sufficient for an elastic polymer to retain its strengthand elasticity, the compliant element 132 may be made of such a polymer.The compliant element 132 may also be made of metal, in the form of, forexample, a garter spring.

The sliding seal assembly includes a sealing ring 170 positioned withinthe seal ring groove 156, which must slide over the inside surface ofthe cylinder 104 as the piston 102 reciprocates lengthwise within thecylinder 104, and also be capable of moving both radially and axiallywithin the seal ring groove 156. Sealing ring 170 is in this embodimenta split ring, having an outer diameter 172, which in the free state (notin contact with any other components) is larger than the inner diameterof the cylinder 104, an inner diameter 174, which in the free state islarger than the outer diameter of the shim 140 and spacer 138, and aheight 176 that is smaller than the height of the seal ring groove 156,enabling relative motion of the sealing ring 170 within seal groove 156between the opposed lands 134, 136. Thus, when the fluid pressure ishigher on one end 106 of the piston 102 as compared to the other end 108thereof, that pressure communicates through a gap 162 which existsbetween the outer wall 198 of clamp ring 164 and inner wall 194 of thecylinder 104, to load the sealing ring 170 against the groove-facingsurface of the land 136 on the side of the seal ring groove 156 oppositefrom that pressure. Additionally, when the fluid pressure becomes higheron the opposite end 108 of the piston 102, i.e., the pressuretransitions so that the pressures on both piston 102 sides 106, 108 areequal and then the pressure on side 108 exceeds that on side 106, fluidpressure on the sealing ring 170 will likewise change, causing thesealing ring 170 to physically move between lands from contact withsecond land 136 when pressure is higher on side 106 to contact withfirst land 134 when pressure is higher on side 108. As the sealing ring170 moves between the lands 134, 136, a small gap between the sealingring 170 and the land 134 or 136 with which it was in contact opens,thereby allowing the volume or space between the inside diameter of thesealing ring 170 and the outside diameter of the spacer 138 to always befilled with fluid at the higher pressure. Where the sealing ring 170 isa split ring (Ramsbottom) or a segmented ring, this higher pressure alsopushes the sealing ring 170 radially outward, so that it substantiallycontacts the inside diameter surface 194 of the cylinder 104. The forceof this contact is substantially proportional to the difference inpressure between the two piston ends 106 and 108. Thus, the pressureloading of the sealing ring 170 against the interior wall 194 of thecylinder 104 is reduced whenever this pressure difference is reduced,resulting in less wear of the sealing ring 120 and energy loss tofriction-generated heat.

The sealing ring may be made of self-lubricating materials such asgraphite or carbon-graphite, possibly filled with PTFE, phenolic,polypropylene, or molybdenum disulfide, or of a polymer such as PTFE,polyimide, phenolic, or polypropylene, possibly filled with graphite,molybdenum disulfide, or PTFE particles. Self-lubricating proprietarymaterials, such as FibereComp™, a carbon fiber composite bearingmaterial, may also be used. If the piston 102 is guided by the cylinderand thus is expected to make sliding contact with the cylinder, thepiston 102 and clamp ring may also be made of such self-lubricatingmaterials. In this case, because the sealing ring 170, clamp ring 164,and the piston 102 may all make sliding contact with the cylinder 104,they may be made of similar or perhaps identical materials that may benecessarily different from the material of the cylinder 104 so as toproduce low friction and wear when sliding over the cylinder 104.Because the sealing ring 170 may nonetheless not produce low enoughfriction and wear if in direct contact with and when sliding over theclamp ring 164 and piston 102, however, there is provided that thecomponents of first and second lands 134, 136, may be made out of amaterial different from the material of the sealing ring 170 thatpromotes low friction and wear as the sealing ring slides radiallyinwardly and outwardly of the seal ring groove 156 formed therebetween.The lands 134, 136 may be made of a material similar or perhapsidentical to that of the cylinder 104. For example, in one embodiment,the seal ring 170, clamp ring 164, and piston 102 may be made fromgraphite and the cylinder 104 and lands 134, 136 from glass. Thus, eachsliding interface, including the sealing ring 170 against the lands 134or 136 and against the cylinder wall 194, and the piston 102 and clampring 164 against the cylinder wall 194 if the piston 102 makes contactwith the cylinder wall 194, is composed of a glass-to-graphite contact.By providing lands 134, 136 and cylinder 104 of a first material, suchas a glass, and the sealing ring 170, piston 102, and clamp ring 164 ofa second material, such as graphite, the sliding interfaces between thesealing ring 170 and lands 134, 136, that between the sealing ring 170and the cylinder wall 194, that between the piston 102 and the cylinderwall 194, and that between the clamp ring 164 and the cylinder wall 194will have the same frictional characteristics. It has been found thatthis arrangement results in a substantial increase in efficiency of thepiston 102-cylinder 104 system when used in a Stirling engineapplication as compared to traditional sealing arrangements, such asclearance seals. If the sealing ring 170 produces low enough frictionand wear if in direct contact with and when sliding over the clamp ring164 and piston 102, however, the lands 134, 136 may not be necessary,and may be omitted from the seal groove assembly 110. Additionally, thesurfaces of the cylinder wall 194 and the lands 134, 136 in contact withthe sealing ring 170 may have a common coating, or the sealing ring 170surfaces in contact with the lands 134, 136 and the cylinder 104, aswell as the surfaces of the piston 102 and clamp ring 164 in proximityto the cylinder wall 194 may have a common coating, such that thematerials of these elements may be structurally optimized for theapplication, but coated to obtain desired sliding properties withrespect to one another.

For simplicity, and as a potential cost-saving measure in lower volumeproduction, the thickness of the spacer 138 may be made equal to thethickness of the sealing ring 170 by making both thicknesses at the sametime and in the same manufacturing setup, and the clearance between thelands 134, 136 and sealing ring 170 established by installing the shim140, which is a thin spacer having the same inside and outside diametersas the spacer 138 but made of shim material whose thickness is equal tothe desired clearance, between one of the lands 134, 136 and the spacer138. The shim material may be a polymer film, such as polyimide, capableof withstanding the temperature of service, and the shim 140 may beinexpensively cut or die-cut from this film. Alternatively, inhigher-volume production, the thickness of the spacer 138 may be madegreater than the thickness of the sealing ring 170 by an amountsubstantially equal to the desired clearance between the lands 134, 136and the sealing ring 170, and the shim 140 not used.

The width and thickness of a split ring (Ramsbottom) or a segmented ringare calculated from consideration of the tolerances of manufacture,fluid pressures, frictional characteristics of the sliding surfaces, andaccelerations, so that: a) The sealing ring 170 remains in contact withthe land 134 or 136 opposite the side of the sealing ring 170 facing thehigher pressure, or, if the pressure reverses, does not lift off theland it is in contact with and contact the other land until close to thetime the pressure reverses; and b) the pressure in the volume 180between the sealing ring 170 and spacer 138 will reliably push thesealing ring 170 outward to maintain substantial contact with thecylinder 104 around the sealing ring's 170 outer diameter, particularlywherever some portion of the side of the piston 102 is locally recedingfrom the corresponding inside surface of the cylinder 104.

The outside diameter of either land 134, 136 is sized so that, under allextremes of the dimensional tolerances, this outside diameter does notcontact the inside surface of the cylinder 104. If the piston 102 isexpected to make contact with the cylinder 104, the clamp ring 164 ispreferably made of the same material as the piston 102, so that theclamp ring 164 may also make sliding contact with the cylinder 104. Thisallows the outer diameter of the lands 134, 136 to be as large aspossible, beneficially minimizing the distance the sealing ring 170overhangs the outside diameter of either land 134, 136. As an additionalcost-saving measure, the dimensions of the lands 134, 136 may besubstantially identical, so that interchangeable parts may be used inmore than one location.

As a further simplification and potential cost-saving measure, the clampring 164 may be eliminated and the compliant element 132 broughtdirectly into contact with the first land 134, provided that the land134 is sufficiently strong, or that the pressure on the face 108 of thepiston 102 opposite the cap 118 is never significantly greater than thepressure on the cap 118, and, in either case, that the tolerances,misalignment or motion of the piston 102 or its components are such thatthe lands 134, 136 (and cap 118 if the cap is not of same material asthe piston 102) do not contact the cylinder 104.

Alternatively, as a further cost-saving measure, the compliant element132 may be eliminated, and the function it had performed be providedinstead by the cap 118, if the cap is constructed with a sufficientlyelastic material.

To assemble the sealed sliding assembly 100, land 136, and then spacer138 and shim 140 are located onto the ledge 166 in notch 112, and thesealing ring 170 is assembled thereover. Land 134 and then clamp ring164 are sequentially placed into notch 112, thereby forming the sealring groove 156 with seal ring 170 therein. Clamp 118, with compliantelement 132 therein, is secured over the end 106 of piston 102 tocomplete the assembly. The seal groove assembly 110 may be assembledonto the piston 102 with the piston separated from cylinder 104, inwhich case a Ramsbottom or a segmented type of seal ring 170 will haveto be first radially compressed, if necessary with a piston ringcompressor tool as used in internal combustion piston engine assembly,to permit insertion of the completed piston assembly into the cylinder104, or while piston 102 is fully positioned within cylinder 104, inwhich case a Ramsbottom type seal ring 170 may be radially compressedmerely by hand during insertion into the cylinder 104. Also, theassembly sequence and construct allows the seal ring 170 to be assembledwithout stretching the seal ring 170 over the outer diameter of thepiston 102, and also allows the seal ring and entire seal grooveassembly 110 to be replaced, if needed, without removing the piston 102from the cylinder 104. Additionally, because the seal ring 170 need notbe stretched over the outer circumference of the piston 102 (or, in FIG.2, distorted to fit into the sealing groove), a solid, not split, ringmay also be employed as the seal ring 170.

In yet another embodiment of the present invention, a combination of acompliant element and a cap having elastic properties may be used. Inyet another embodiment, as shown in FIG. 3, the compliant element may beeliminated, and the function it had performed be provided by one or moresprings 260, such as disk or Belleville springs located under the headsof the fasteners 122, so as to allow the cap 118 and seal grooveassembly 110 to be clamped to the piston 102 by the force of the springs260. A substantially controlled and circumferentially uniform amount offorce is exerted, provided that the surfaces in contact are flat enough,while absorbing the accumulation of the dimensional tolerances in thesecomponents.

FIG. 2 shows an, alternate embodiment of a sealed sliding assembly 200of the present invention likewise useful for sealing a sliding interfacebetween a rod and a bushing rather than between a piston and a cylinder.In this embodiment, the roles of the piston and cylinder in the firstembodiment are reversed, with the inside surface of the cylinderbecoming the outside surface of the rod 202, and the outside surface ofthe piston becoming the inside surface of the bushing 204. As with thesealed sliding assembly of FIG. 1, either the rod 202 or the bushing204, or both, may be moving with respect to a stationary reference. Allof the components function in the same way as those of the sealedsliding assembly 100, except that the higher pressure in the volumebetween the outside diameter 210 of the seal ring 212 and the insidediameter 214 of the spacer 216 causes the seal ring 212, if the sealring 212 is a split ring (Ramsbottom) or a segmented ring, to be pushedradially inwardly (in the direction of the rod 202), so that itsubstantially contacts the outside diameter 220 of the rod 202.

Referring to FIG. 4, the sliding seal assembly of FIG. 1 may be modifiedto include a ring pack 300 formed from certain components of the sealgroove assembly 100 of FIG. 1. In this embodiment, the notch 330 intothe piston 332 of FIG. 3 is extended as compared to that of notch 112 ofpiston 102 of FIG. 1, and a ring pack 300 may be formed by assembling astack of sealing rings 302, shims 304, and spacers 306 individuallyalternating with lands 308 a-f into the notch 330, and the assembly isheld against the ledge 334 of the notch 330 adjacent the end of thepiston 332 with a single clamp ring 310 having an outside diameter 312slightly greater than the outside diameters 314 of the lands 308 andinstalled between the uppermost land 308 a and a compliant element 314held by a cap 316 removably fastened to one end 320 of the piston 332,so as to prevent the outside diameters of the lands 308 from contactingthe cylinder. This ring pack 300 requires lands 308 that are strongenough to withstand the force resulting from the worst-case division ofthe fluid pressure across the piston and the force resulting fromaccelerating the mass of the clamped components. Again, as with theembodiments shown in FIG. 1, the seal rings 302 of this embodiment areintended to move through a gap within the seal groove created by thespacing between the opposed faces of adjacent lands 308 of each groovebeing larger than the thickness or height of the seal ring 302, and, ifthe seal ring 302 is of the Ramsbottom or segmented types, a gap betweenthe seal ring 302 and the base of each seal groove may be accessed bythe higher pressure fluid to increase the sealing force of the seal ring302 against the cylinder wall 340. As with the alternate embodiment ofthe sealed sliding assembly 200 used for sealing a sliding interfacebetween a rod and a bushing rather than between a piston and a cylinder,where the roles of the piston and cylinder are reversed, the ring packembodiment may be applied to the sealed sliding assembly 200.

The embodiments of the invention shown and described herein provide manyadvantageous features. For example, the components in sliding contactare able to run without liquid lubrication. Use of a seal ring 170 asthe sealing method allows a significantly shorter piston and cylinderfor the same piston stroke length compared to a piston and cylindersealed by a clearance seal, and the tolerances that are critical involveprimarily flatness and parallelism, which may be achieved inexpensivelyas compared to the tight diameter and cylindricity tolerances necessaryto produce a good a clearance seal. By clamping the components of thesliding seal assembly using a compliant member such as an o-ring, theclamping force on the elements may be well-controlled or limited to alow value, thus allowing these components to be made of fragilematerials, such as glass or carbon-graphite, while at the same timeallowing the fasteners 122 to be secured against loosening by anysuitably robust means, independent of the amount of clamping force,including, if they are threaded fasteners, being tightened to a hightorque or otherwise secured by a thread-locking means, and allowing theaccumulation of the dimensional tolerances in these components to beabsorbed while maintaining a consistent and predictable amount ofclamping force.

The lands 134, 136, and 308 may be constructed from float glass (e.g.Schott's Borofloat), which inherently and inexpensively providessufficient flatness, smoothness, and parallelism of the flat surfaceswith minimal or without any further grinding, lapping, or polishingoperations, and which is compatible with the materials used herein forthe seal rings 170, 212, and 302. The inside and outside diameters ofthe float glass lands may be produced by precision abrasive waterjetcutting, which is a relatively inexpensive process for achievingsufficient dimensional accuracy. They may also be constructed ofporcelain enamel coated metal, preferably a metal such as Kovar which isstronger and stiffer than glass and whose coefficient of thermalexpansion is close to that of the porcelain enamel, which, if the flatsurfaces are not flat enough, could be inexpensively Blanchard ordouble-disk ground to achieve the required flatness

It is understood by those skilled in the art that certain components ofthe assemblies and subassemblies described herein may be omitted orinterchanged within the sealed sliding assembly of the presentinvention.

1. A sealing assembly configured for the sealing of a sliding interfaceof a first member and a second member wherein said first member and saidsecond member reciprocatingly move with respect to one another, saidfirst member having an outer circumference of a first diameter and saidsecond member having an inner circumference of a second diameter, saidsealing assembly including: a seal ring groove received on one of saidfirst or second members, said seal ring groove including opposed landscomprised of a material different from that of said first or secondmember within which it is located, said seal ring groove defining acircumferential base and a span of a distance L between said lands; aseal ring received in said seal ring groove, said seal ring having aspan smaller than L, a free outer diameter greater than said outerdiameter of said first member and an inner diameter greater than thediameter of said base of said seal ring groove where said seal ringgroove is received within said first member, or a free inner diametersmaller than said outer diameter of said first member and an outerdiameter smaller than said diameter of said base of said seal ringgroove where said seal ring groove is received within said secondmember, such that a gap may be maintained between said seal ring andsaid base of said seal ring groove within which said seal ring islocated; wherein said seal ring is free to move between said first landand said second land in response to changes in the pressure on opposedsides of said seal ring.
 2. The sealing assembly of claim 1, whereinsaid sealing assembly components are fully self lubricated with eachother.
 3. The sealing assembly of claim 1, wherein said first member isa piston and said second member is a cylinder, and said pistonreciprocates within said cylinder.
 4. The sealing assembly of claim 1,wherein said first member is a rod and said second member is a bushing.5. The sealing assembly of claim 1, further including a clamp ring and aland in contact with one another, wherein said clamp ring providessupport to maintain the position of said land in said seal ring groove.6. The sealing assembly of claim 1, wherein said first member and saidseal ring are made of substantially similar materials.
 7. The sealingassembly of claim 1, wherein said seal ring and said lands are made ofsubstantially different materials.
 8. The sealing assembly of claim 1,wherein said seal ring groove includes first and second lands, and ashim and a spacer located between said lands, and said seal ring andsaid spacer have the same span between their substantially parallel flatsurfaces.
 9. The sealing assembly of claim 1, wherein fluid at thehigher of the pressures acting upon opposed sides of said first memberis present in the gap formed between said seal ring and said spacer. 10.The sealing assembly of claim 1, wherein said seal ring is comprised ofa first material, and said lands are comprised of a second material. 11.The sealing assembly of claim 10, wherein said first member and saidsecond member are comprised of different materials, and said seal ringand said first or second member having said seal ring groove extendingtherein are comprised of the same material.
 12. A method of sealing asliding interface between a first member and a second member, whereinsaid first member includes a seal ring groove therein on a surfaceabutting a surface of said second member, said seal ring groove having abase and having opposed lands comprised of a material different fromthat of said first member therein, said opposed lands separated by aspan L, and a seal ring having a surface received within said seal ringgroove, facing and spaced from said base of said seal ring groove andhaving a span smaller than L, including the steps of: applying apressure on a first side of said first member that is greater than thepressure on a second side of said first member, the pressure causingsaid seal ring to move within said seal ring groove into engagement withthe land of said seal ring groove closest to said second side of saidfirst member; experiencing a change in the relative fluid pressure onsaid first and second sides of said first member, such that the pressureon said second side of said first member becomes greater than that onsaid first side of said first member, and causing said seal ring to movewithin said seal ring groove into engagement with the land of said sealgroove closest to said first side of said first member; and, wherein theseal ring may expand and contract radially, and whenever there is adifference in pressure between said first and second sides of said firstmember, establishing a fluid passage from the side of said first memberhaving the higher pressure, through the gap established when said sealring moves between said lands away from the side of said first memberhaving the higher pressure, to the region in said seal groove betweensaid seal ring and said base of said seal groove, such that, as thepressure increases on the side of said first member having the higherpressure, the force exerted by said seal ring against the adjacentsurface of said second member is increased.
 13. The method of claim 12,further including the step of providing a split ring style seal intosaid seal groove, said split ring having a free diameter such that saidseal ring will be spaced from said base of said seal groove andnaturally contact the adjacent surface of said second member.
 14. Themethod of claim 13, wherein said first member is a piston and saidsecond member is a cylinder.
 15. The method of claim 13 wherein saidfirst member is a bushing and said second member is a rod.
 16. Themethod of claim 12, wherein said seal groove subassembly includes aclamp ring and one of said lands in contact with each other, whereinsaid clamp ring provides support to said land.
 17. The method of claim12, wherein said first member and said seal ring are made ofsubstantially similar materials.
 18. The method of claim 12, whereinsaid seal ring and said lands are made of substantially differentmaterials.
 19. The method of claim 12, wherein said seal groove includesfirst and second lands, and a shim and a spacer located between saidlands, and said seal ring and said spacer have the same span betweentheir substantially parallel flat surfaces.
 20. A sealing assemblycomprising: opposed first and second lands having a gap there between,said gap having a first span and forming a seal groove having a basetherein and an opening opposed to said base; and a seal ring receivablewithin said seal groove, said seal ring having a second span less thansaid first span and opposed circumferential faces, wherein, in a freestate, the diameter of one of said circumferential faces is greater thanthe diameter of said base, and the second of said circumferential facesextends beyond at least one of said lands at a position thereof distalto said base.